Fig. 1. Seven-layer skin model

Fig. 2. Optical model of fiber-optics probe and skin tissue

Fig. 3. Monte-Carlo simulated photons transmission in seven-layer skin model. (a) Relationship between the radial distance r, the detection depth z and the light energy flow rate F; (b) changes energy of fluorescent light source with the radial distance r; (c) relationship between the detection depth z and the energy flow density Φ(z) at different skin layers

Fig. 4. Effects of structural parameters of fiber-optics probe on fluorescence intensity by simulation. (a) Effect of source-collection fiber-optics separation distance D₁ on fluorescence intensity; (b) effect of core diameter of collection fiber-optics D₂ on fluorescence intensity; (c) effect of distance between fiber-optics probe and skin on fluorescence intensity; (d) effect of numerical aperture of collection fiber-optics on fluorescence intensity

Fig. 5. Design of fiber-optics probe

Fig. 6. Experimental setup of fluorescence spectrum detection system and experimental result. (a) Experimental setup; (b) fluorescence intensity change rate of NADH detected in experiment